Remember walking to school on your own for the first time? The journey no doubt began with a mixture of elation and fear; there was a busy road to cross and you weren’t sure when to launch yourself into the roaring maelstrom. But you took the plunge – and somehow survived.

Every year, however, hundreds of children get it horribly wrong. Last year, 26 child pedestrians died on British roads, and 1,620 were seriously injured, according to the latest Department for Transport figures. New research is beginning to explain why some children get it so wrong, with important implications not just for parents and children, but motorists, too.

Scientists at the Department of Psychology, Royal Holloway, University of London, have discovered that primary-age schoolchildren cannot accurately see, or judge, the speed of vehicles travelling above 25mph. In fact, six- to 11-year-olds might sometimes not be able to tell that a vehicle is approaching owing to a trick of the mind that also affects adults, although it is far more pronounced in children.

As Professor John Wann, a 55-year-old driver, cyclist and motorcyclist who led the research, explains: “It’s not a matter of children not paying attention but a problem related to low-level visual detection mechanisms. Even when children are paying very close attention they may fail to detect a fast-approaching vehicle.”

The speed illusion works like this: everyone gauges the speed of an approaching object by assessing how quickly its image gets larger, its “looming rate”, and everyone has a threshold in their ability to detect it.

But, alarmingly, the faster a car is going, the lower its “looming” rate can appear, with the phenomenon especially acute if you’re under 11 or over 75. While adults can make reasonably accurate judgments for a car travelling at up to 50mph, the judgment of primary-age children becomes unreliable once the speed rises above 25mph.

Prof Wann believes that the answer lies in traffic regulation – and that means more controversial 20mph zones. “Children make risky crossing judgments when vehicles are travelling at 30mph or 40mph,” he says. “Worse, the vehicles they are more likely to step in front of are the faster vehicles that are more likely to hurt them. So putting 20mph speed limits in sensitive areas such as outside schools, when motorists can see a reason for them, would remove that threat.”

Prof Wann is persuasive about the benefits: “Travelling one mile through a residential area at 20mph versus 30mph only adds 60 seconds to your journey time, far less than negotiating a junction or stopping at a traffic light.”

However, he cautions against imposing too many 20mph zones. “The majority of drivers apply some level of conformity to speed limits,” he says. “They might not all drop to right below 20mph but most get close and that makes a big difference. You have to be particularly nonconformist not to drop your speed at all when you enter a lower-speed zone. No one wants a child on their bonnet.”

Prof Wann thinks too many 20mph zones can dilute their effectiveness, as motorists fail to recognise they are in a “high-risk area” and are less likely to comply. Peter Rodger, chief examiner of the Institute of Advanced Motorists, agrees. “Most motorists back 20mph in the right place,” he says. “But if they are introduced where it feels wrong – where there are good sight lines and wide roads – it brings 20mph zones into disrepute. Blanket go-slow zones will not help.”

Prof Wann says the argument extends to enforcing zones with humps or speed cameras. There are areas where they may be warranted, but ultimately, a nationwide solution lies in most drivers recognising that 20mph signage is in place because there is an elevated risk in the zone they are entering.

Prof Wann’s study of more than 100 children found little difference between the ability of those aged six, seven, eight or nine to discern looming but it began to improve for 10- to 11-year-olds. However, the neural mechanisms don’t fully develop until adulthood.

Worryingly, if an oncoming vehicle is even slightly outside a child’s main field of vision, or if the child is also moving, their detection levels plummet even further.

“Our findings have important implications for road-safety policy,” says Prof Wann. “They converge with evidence that the risk of pedestrian accidents involving children is nearly three times higher in places where mean speeds exceed 25mph compared with places with lower speeds.”

Not all motorists will like it but the research underlines work by the Department for Transport in 1999, which showed that reducing traffic speed to 20mph led to a 50 per cent drop in the number of six- to 11-year-olds killed or seriously injured. That’s partly due to the speed of impact, because pedestrians have a 90 per cent chance of surviving being hit by a car at under 20mph but a less than 50 per cent chance of surviving at 28mph or higher.

“It seems clear-cut,” says Prof Wann. “Driving in excess of 20mph in a residential or school area not only increases the potential severity of any impact with a pedestrian, but also increases the risk that a child will injudiciously cross in front of your car.”